剑指Offer56-按之字形顺序打印二叉树

请实现一个函数按照之字形打印二叉树，即第一行按照从左到右的顺序打印，第二层按照从右至左的顺序打印，第三行按照从左到右的顺序打印，其他行以此类推。

/* public class TreeNode { int val = 0; TreeNode left = null; TreeNode right = null; public TreeNode(int val) { this.val = val; } } */
import java.util.Stack;
import java.util.ArrayList;
public class Solution {
   
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
   
        ArrayList<ArrayList<Integer>> list=new ArrayList<ArrayList<Integer>>();
        if(pRoot==null)
            return list;
        Stack<TreeNode> oddStack=new Stack<>();
        Stack<TreeNode> evenStack=new Stack<>();
        oddStack.add(pRoot);
        boolean flag=true;
        while(!(oddStack.isEmpty()&&evenStack.isEmpty())){
   
            ArrayList<Integer> temp=new ArrayList<>();
            if(flag==true){
   //奇数行，odd中元素节点的孩子按先左孩子孩子后右孩子顺序入even
                while(!oddStack.isEmpty()){
   
                    TreeNode t=oddStack.peek();
                    temp.add(t.val);
                    if(t.left!=null){
   
                        evenStack.add(t.left);
                    }
                    if(t.right!=null){
   
                        evenStack.add(t.right);
                    }
                    oddStack.pop();
                }
                list.add(temp);
                flag=false;
            }else{
   //偶数行,even中元素节点的孩子按先右孩子孩子后左孩子顺序入odd
                while(!evenStack.isEmpty()){
   
                    TreeNode t=evenStack.peek();
                    temp.add(t.val);
                    if(t.right!=null){
   
                        oddStack.add(t.right);
                    }
                    if(t.left!=null){
   
                        oddStack.add(t.left);
                    }
                    evenStack.pop();
                }
                list.add(temp);
                flag=true;
            }
        }
        return list;
    }
}